zandalman

Among the emerging excess of massive, bright galaxies at Cosmic Dawn (z > 9) seen by the James Webb Space Telescope, several exhibit spectral features associated with active galactic nuclei (AGN). These AGN candidates suggest that supermassive black holes (SMBHs) grow rapidly in the early Universe. In a series of numerical experiments, we investigate how SMBHs grow within and influence the most massive galaxies at Cosmic Dawn using cosmological hydrodynamic zoom-in simulations run with the adaptive mesh refinement code RAMSES. Our suite of simulations explore how super-Eddington accretion, seed mass, and the strength of feedback influence SMBH-galaxy co-evolution in the early Universe. We find that SMBH growth is sensitive to stellar feedback which generates a turbulent-multiphase interstellar medium (ISM) that stochastically starves the SMBH. In the absence of AGN feedback, we find that the SMBH is starved ~50% of the time after the onset of star formation in the galaxy. SMBH growth can become self-regulated by AGN feedback if the SMBH becomes massive enough, either by accretion or seeding, for its feedback to dominate the surrounding nuclear region. We find no evidence of galaxy-scale, AGN-driven quenching in the star formation rate (SFR) across all simulations in our suite.

SMBH mass evolution in our suite of cosmological zoom-in simulations of a massive galaxy at Cosmic Dawn in RAMSES. The suite includes simulations with/without AGN feedback (solid/dashed lines) and across a range of maximum Eddington factors (lam_Edd) and initial SMBH masses. For context, we also show empirical SMBH mass estimates from JWST. The zoom-in panels show snapshots of the projected density field within a 500 pc region around the SMBH. The SMBH stochastically samples the multi-phase ISM, resulting in alternating phases of slow Bondi-limited accretion in hot-diffuse regions (starve mode) and fast Eddington-limited accretion in cold-dense regions (feast mode). AGN feedback only regulates the SMBH growth if the SMBH becomes massive enough to homogenize the ISM in the nuclear region.

Supermassive Black Hole Growth in Massive Galaxies at Cosmic Dawn

Abstract